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Missing YouTube video thumbnails [fixed] (self.meta)

submitted 2 years ago* (last edited 1 year ago) by necropola to c/[email protected]

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Does anybody know why and when thumbnails for YouTube videos are shown or not? It appears to depend on the lemmy instance the posts are served from:

Without Thumbnails

With Thumbnails

Update: It's not only YT thumbnails which aren't shown. This is your post about the free 24 slot bag as shown on lemmy.wtf (without thumbnail), lemmy.world (without thumbnail) and feddit.de (with thumbnail):

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[–] necropola 3 points 2 years ago (1 children)

But you are getting the same results as me when trying the links? The first 2 have thumbnails and the last 2 don't, right?

[–] [email protected] 3 points 2 years ago (2 children)

Exactly.

[–] necropola 3 points 2 years ago* (last edited 2 years ago) (1 children)

That's really weird. I already went through the issue tracker on GitHub for both the lemmy backend as well as the frontend, but couldn't find anything. I also checked the documentation whether there is a configuration option somewhere. Nothing.

~~My guess is that the thumbnail is extracted (read from the opengraph tag available via the posted URL) in the frontend (and not the backend).~~ (wrong guess)

The only thing I could find on the issue tracker which might be related is this:

https://github.com/LemmyNet/lemmy-ui/issues/709

[–] [email protected] 1 points 2 years ago* (last edited 2 years ago) (1 children)

I have no idea why it is happening. The only thing I can think of is Cloudflare tunnel, but why would that keep the thumbnails from loading? I send a message to the admin of Lemmy.world.

edit: I am also trying to troubleshoot why users from kbin.social can't subscribe to here and vice versa.

[–] necropola 3 points 2 years ago (1 children)

I was able to subscribe from lemmy.world to kbin.social (yesterday or the day before). I tried it on another account from feddit.de today and it did not work. My guess is a problem at kbin.social.

[–] [email protected] 1 points 2 years ago* (last edited 2 years ago) (1 children)

This works:

This doesn't work:

The difference between the two communities at lemmy.world, is that c/selfhosted has been around for a long time and c/xcode was created just a few days ago. It seems that only communities that initially connected with kbin.social work, but not new communities.

[–] necropola 3 points 2 years ago* (last edited 2 years ago)

I see you have been discussing this with the people & mod of the GW2 magazine on kbin.social already. To me it really seems to be an issue on their side. As I mentioned above: I currently cannot subscribe from feddit.de to their GW2 magazine, either.

Update: I was now able to subscribe to their GW2 magazine from feddit.de, but it does not display any posts.

[–] necropola 3 points 2 years ago (1 children)

I also found this

https://github.com/LemmyNet/lemmy-ui/issues/20

There is an environment variable LEMMY_UI_DISABLE_CSP (default : false) to configure lemmy-ui. Do you set this on your instance or do you set a Content-Security-Policxy Header somewhere in your webserver/nginx config?

[–] [email protected] 1 points 2 years ago (1 children)

I just use the settings as it is shown in the installation guide for Docker: https://join-lemmy.org/docs/en/administration/install_docker.html

[–] necropola 3 points 2 years ago* (last edited 2 years ago) (1 children)

OK. Looks like the CSP headers are the same on working and not working instances.

What I found surprising is that chrome loads the thumbnail without accessing the actual YT URL (contrary to what I expected) from the "pictrs" server of the instance serving the post. Which means that the thumbnail gets only extracted once and is then stored along with the post.

[–] necropola 3 points 2 years ago* (last edited 2 years ago)

Brainstorming

Thumbnail extraction definitely happens in the backend.
- But when does it happen?
- Only when creating the post?
- Or also when federating a post to a new instance?
- PR which replaced iframely ➡ https://github.com/LemmyNet/lemmy/pull/1706
- Now backend uses fetch_site_metadata ➡ https://github.com/LemmyNet/lemmy/blob/main/crates/api_common/src/request.rs
- ... which evaluates the opengraph (og:*) meta tags from a linked HTML document whenever a post is created or updated
Thumbnails do neither work on lemmy.wtf nor lemmy.world but work on feddit.de
- Does feddit.de extract the missing thumbnail when creating/updating the post? ➡ Yes, I think so
- Or does it expect the thumbnail to be transmitted alongside the post? ➡ No, I don't think so
lemmy.world does not use cloudflare (I think) but they are also (like lemmy.wtf) using docker (I think)

Also Not Working on lemmy.world

https://lemmy.world/c/music

But does on feddit.de

https://feddit.de/c/[email protected]

It's not only YT thumbnails which aren't shown. This is your post about the free 24 slot bag as shown on lemmy.wtf (no thumbnail), lemmy.world (no thumbnail) and feddit.de (with thumbnail):